Telephone reinforcing-circuit.



0. D. LANNING.

TELEPHONE REINFORGING CIRCUIT.

APPLIGATION FILED AUG. 2, 1911.

Patented Mar. 9, 11915.

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TELEPHONE REINFORCING-CIBCUIT.

Specification of Letters Patent.

Patented Mar. 9, 1915.,

Original application filed December 26, 1905, Serial No. 293,216. Divided and this application filed August 2, 1911. Serial No. 641,946.

To all whom it may concern Be it known that I, CHARLES D. LANNING, a citizen of the United States, and a resident of Boston, in the county of Suffolk and Commonwealth of Massachusetts, have invented an Improvement in Telephone Reinforcing- Circuits, of which the following description, in connection with the accompanying drawings, is a specification, like characters on the drawings representing like parts.

My invention relates in general to cooperative arrangements of telephone line circuits or conductors forming part of line systems with a subsidiary circuit arrangement; the latter actuated by some conductor operatively related to the line and containing instrumentalities for setting up new currents, and being connected to the line or said conductor in such manner as to reinforce the original line current by adding thereto the new current set up by the reinforcing arrangement. Such a circuit system is generally, though not necessarily, within the class of closed-circuit telephone repeating arrangements as distinguished from circuit systems in which the circuit connections are made and broken responsively to the passage of voice-caused currents from one terminal station to the other and reversely. Specifically, in such closed circuit arrangements, my invention may be advantageously embodied in telephone repeating systems in which the line system from terminal station to terminal station is not divided into reciprocally arranged sections, the latter being shown in the early patent to Gilliland, 247,631 of 1881, and later developments thereof.

Preferably my invention provides a complete circuit from terminal station to terminal station, free of bridge connection to the line system, whereby the line system is retained in such form as to avoid splitting or weakening the current effects thereon; but broadly my invention provides a system for circuiting a telephone reinforcing arrangement serially to a conductor forming part of a line system without any bridge or split connections intervening in said conductor between the connections of the repeating instrumentalities thereto, although said repeating arrangement may not be directly related to one of the main line conductors. In general in the Working out of effective telephone repeaters it has been found that such closed circuit arrangements are simpler and more eflicient than arrangements embodying make-and-break devices for controlling the circuit connections, for such closed circuit arrangements maintain the repeating instrumentalitios in the same general relation to the line as obtains with the usual terminal transmitting and receiving devices. More over in such closed circuit arrangements it has been found that the preferable form is that which maintains the circuit undivided from terminal station to terminal station; that is, not divided into reciprocally arranged sections with reciprocally arranged relays or repeaters acting from one section into the other as shown in said patent to Gilliland. In the latter form a repeating instrument necessarily has to set up in the distant line section a new current and nothing is gained unless the new current is stronger than the original voice-caused current in the line section energized by the latter. In the form of closed circuits, however, which are not reciprocally arranged, the action is strictly that of current reinforcement, the original voice-caused current passing over the whole line system and the repeater current being added thereto so as to build up a stronger line energy. A number of such systems have been devised embodying bridge circuits in the main line or a plurality of bridge circuits, in which bridge circuits part or all of the repeating instrumentalities are connected. That is, the telephone repeating apparatus usually includes a receiving element and a transmitting element operated thereby and in such bridge arrangements either the receiving element has been connected to one line bridge and the transmitting element operated thereby to another line bridge; or one of said elements to a line bridge and the other to a line conductor. This obviously means that the currents intended for line actuation are split in the various circuit portions formed by the bridge and not only is the line current intended to energize the repeater thereby weakened but also the new line current set up by the repeater is weakened so far as affecting the ultimatevoice-current receiving instrument which latter it is the purpose to energize more strongly.

When I herein refer to bridge circuits between the main line conductors or otherwise it will be understood that I intend the term to be inclusive both of conductive and inductive bridges, as well known and frequently illustrated in this art.

Preferably I connect the repeating instrumentalities serially to a line conductor, that is, connect the receiving element and the transmitting elements, each and both, in series to a line conductor and this obviates all weakening of current effects such as results from bridge circuit connections; and even if, for any reason, I connect the repeating devices to a conductor not one of the main line conductors but operatively related thereto, I so connect them serially to said conductor without any bridge or split circuit intervening therein. I also preferably connect each of the repeater elements to the related conductor or line by undivided series connection therewith dispensing with divided circuits introduced for the purpose of aflording balancing arrangements. Such balancing arrangements have been introduced for the purpose of avoiding what is known as reaction on telephone repeater circuits. This is an automatic effect in the form of current action, set up upon such closed circuit repeater lines, whereby a continuous current wave is formed and a singing sound set up in the receiving instruments, which of course results in rendering the whole line completely or partially inoperative in a commercial sense. Such reaction results from the fact that a telephone receiving and transmitting device are operatively connected each to the other in such closed circuit arrangements; that is, are connected so that any energization of the receiving element not only operates (as it should) the transmitting element, but conversely any energization of the transmitting element reacts upon and energizes the receiving element. This effect is closely analogous to that which has been observed as resulting from the placing of the ordinary receiver close to the usual transmitter. In such position, if the latter is in a sensitive condition, and is initially energized by any air wave, the energy set up acts through the line upon the receiver which in turn acts upon the transmitter and sets up a continuous reaction and consequent singing. A good deal of attention has been paid to this phenomenon in order to work out an explanation but it would seem to be due undoubted-1y to the fact that the passage of the electrical impulse over the line which energizes the receiver and the passage of the air wave from the receiver to the transmitter are not synchronous or simultaneous, but sequential; so that the transmitter, which would normally become quiescent, is again energized by the air wave impinging upon it from the receiver action caused by the original transmitter action; the electrical impulse passing over the line at the assigned speed or flow of electrical current over a conductor, and the air wave passing from the receiver to the transmitter at a very greatly lesser speed; the speed of one, of course, being many thousands of times as great as the other. The factors causing telephone reaction in closed circuit telephone repeater arrangements are in principle substantially the same. If the line system is split into portions by reciprocal arrangement or bridge arrangement, then, entirely apart from other factors, reaction may result from the fact that the inductance and other electrical elements of the circuit portions are different, and the current wave passing over such respective portions is differently affected both as to time and form; and, again reaching the telephone receiving element through the closed circuit system, these different current effects cause a new excitation thereon. It has been attempted to overcome this difficulty by introducing balancing arrangements and other form of split circuit arrangements but they obviously tend to impair the designed effect of the repeater arrangement and further render it necessary that there be some manual control of the system as different terminal connections are made.

With my invention as herein disclosed provision is made for so relating the telephone repeating arrangements to the line that synchronous and harmonious reinforcement of the line current can be had without any such effects as above described.

Since all commercial telephony substantially speaking is by means of alternating currents, in combination with which the receiving element (whether of voice-receivers or repeater-receivers) is an initially energized magnet responding separately to the opposite phases of the alternating current (and thereby constituting a true polarized device); and since in the usual forms of transmitting element of the repeater a mechanical vibrator such as a spring in the form of a diaphragm is generally used, I have found it is very essential in order to avoid reaction that the internal connections in the repeater systems should be such that whatever movement of the said repeater diaphragm is caused by the original voicecaused current receiver (that is, a movement toward or away from the receiving magnet) the other connections, should be such that the repeater will impress upon the line a current efl'ect which, received by the repeater-receiver, will have an action thereon to cause the same movement of said diaphragm. If this is not done, inertia effects in the repeater-diaphragm and associated armature acted upon by the repeater-receiver magnet will be such as to tend to set up a continuous movement or vibration of said diaphragm and resulting reaction upon the line; each receiver-caused current variation reacting through the line to create an opposite current variation.

\Vith the foregoing general explanation my invention will be clear from the annexed drawings and following detail specifications.

In the drawings I have illustrated my invention by means of circuit maps, the representation of the various apparatus being largely conventional.

Figure 1 represents a telephone line With its terminal stations, of the local energy type, and two reinforcer arrangements serially related thereto, both the receiving and the transmitting element of the reinforcer being serially and inductionally related to the line. Fig. 2 is similar to Fig. 1 except that the receiver elements of the reinforcers are connected in metallic series to the line.

In detail in Fig. l (1 represents a metallic circuit main line and A and B in general the terminal stations each comprising a variable resistance transmitter t in series with the local battery I) and the primary of the induction coil 0. The secondaries of the said induction coils are in series with the main line which at the local stations has also in series the receivers 1', 7'. As to the two reinforcing arrangements, the connections are the same in each case and a description of one will suffice. The line is in series through the primary of the stepdown transformer z and the secondary of the step up transformer g. The primary of the step-down transformer z is in series with the winding of the receiving magnet h. This receiving magnet acts upon an armature connected to the vibratory electrode of a transmitting microphone f, which has in series the local battery 6 and the primary d of the step-up transformer g. The representation of the repeater apparatus comprising the receiving element It and the transmitting element 7 with its connections is conventional and it will be understood that any form of repeater apparatus may be employed. It will be seen that original voice-caused line currents will energize the receiving magnet h which in turn will, through the actuation of the microphone 7 set up varying currents in the primary 0! which will in turn inductionally impress new current effects upon the line through the transformer g.

In Fig. 2 the connections are the same as in Fig. 1 except that the line is in metallic series with the Winding of the repeater-receiving magnet it instead of being inductionally related thereto. It will be seen that in this form shown the repeater arrangement is connected purely in series to the line and that the latter is maintained in an unbroken condition, that is free of any split or bridged circuit connections therein. This is the preferable form of my invention, although the repeater instrumentalities might be serially connected to a single conductor forming any part of the line system and operatively related thereto in any manner, such conductor in such case being maintained free of split or bridged circuit con nection, interior of the connections of the reinforcing arrangements thereto. By my invention in its preferable form, therefore, it will be seen that not only are all reciprocal arrangements obviated, with the consequent necessity of splitting the main line into opposed terminal sections, but also that the main line is maintained in unbroken form so that all current effects impressed upon it either by the terminal stations or the repeater arrangements are active to energize the whole line and thereby reach as desired the distant listening instruments. Atwvhatever point therefore the repeating arrangements may be placed and whatever terminal connections may be made in actual use, the line is retained in a unitary condition; and if the mechanism forming part of the repeater arrangement be of appropriate' design so as to eliminate electro-magnetic and mechanical lag elements and produce action of the repeater upon the line synchronous with the action of the line upon the repeater; and further if the connection of the repeating system to the line be harmonious, that is, connected so as to impress upon the line a current phase harmonious with the original line current phase acting upon the repeater; efficient cumulative reinforcement of the line current will be had.

It will be obvious that as many separate reinforcing arrangements as may be desired may be connected to the line at any desired point or points, each being independent of the other but each being necessarily so connected as to synchronously and harmoniously cooperate with the line.

I have above discussed in general the causes of reaction in telephone repeater closed circuits. Such divided circuits as are inherent in reciprocally arranged circuits are, of course, obviated by my invention as disclosed herein. Similarly in the form preferably employed by me as herein disclosed, the effects inherent in bridge systems are avoided; that is, both the weakening of line current effects by bridge or split circuit formation and the reaction due to the various resulting current effects had from the differently constituted circuit portions as dependent upon' the inductance or other electrical elements thereof.

By the application of my invention it is resulting from various lag elements as above noted) tends to destroy the wave forms and to produce in the place of any single peaked wave a double peaked wave, which obviously means renewed excitation of the repeaterreceiver. By harmonius action I have, as above indicated, particular reference to the relation of two alternating currents, one impressed upon the other and to two factors. The first factor is the relation of the wave form received by the repeater circuits from the line and the wave form re-impressed upon the latter by the former. These obviously should be the same; which means that the same phase (positive or negative) received by the repeater eireeib ebeuib be reirr pressed by them en the line. This it will peater-receiver shall be re-impressed by therepeater transmitter on the line. If this is not done, the same distortion of wave form will or may result as results from lag fac tors; that is, the creation of double peaked wave forms in place of single peaked wave forms with consequent reaction. A second factor relating to harmonius circuiting has to do with the internal connections in the repeater circuits. Assuming as constituent elements of the repeating instrumentalities an initially magnetized receiving element, responding differentially to the phases of an alternating current (constituting therefore, as does the commercial receiver when used with alternating currents, a true polarized device) and a local direct current varied in value by such receiving device and in turn operating to vary or produce a line current that finally reacts on the repeater-receiver, it is important that the connection of the circuit carrying the local current to the repeater-receivergoverned current varying means affecting such local current shall be such that any current impression put on the line by the repeater will produce in the said local current the change necessary to produce said last mentioned current impression. To make this clear, if the repeater local-current varying-device is a variable resistance microphone acted upon by an armature in the field of an initially magnetized electro-magnet adapted to be energized by the main line, then not only must the terminal connections of the line and the repeater circuits be harmonious, but the connections of the local circuit to said current varying device must be such that any given movement of the said armature shall produce an immediate local direct-current effect (and consequent line current effect) that, ultimately, reacting on the said magnet through the line, will produce the same movement of said armature. If this is not done a condition is produced analogous to that existing in the interrupter of induction coils; that is, each change of movement by the armature tends, through the connections and magnetic arrangement, to produce an opposite movement thereof, and re-active singing of the line will result. It will be seen that these two factors are cooperative and must have attention in order to secure harmonious action and proper reinforcement of line-errrrerrt by repeebee-reused eurrebb 'bbe berrbirbb eebrrebebb el' be re peater system to the line must be such as to give harmonious action; and to accomplish this the line must be so connected to the repeater-receiver, and the local current of the repeater must be so connected to the repeater current-varying device and also to the repeater-transmitting-induction coil that any given current impulse received by the repeater and causing a given character of variation of the repeater local current will act to reimpress on the line a new current impulse (which must eventually act again or react upon the repeater receiver) of such character that the same variation of the repeater local current will be caused. \Vith this done and synchronism of action also obtained, obviously there can be no distortive re-action for the condition necessary to cause harmful, voice-eurrent-distortivc re-action is eliminated and prevented.

It will be evident from the foregoing that in the serially connected repeater or reinforcing circuits and instrumentalities which I have disclosed I have provided means whereby a transmitter line may be kept in the normal unitary connection from terminal to terminal and telephone currents thereon reinforced by harmonious connection and synchronous action, so that the disturbing and variable factors present in bridged or reciprocally arranged repeaters are avoided. The action of the line on the repeater and of the repeater on the line is obviously best had through undivided circuits.

All effort to avoid action of the repeatercaused line current back on the repeater receiver is set aside, through the recognition of the fact that where telephonic receiving and transmitting elements are in electrical connection as in closed circuit reinforcing systems such back action cannot be obviated but is inherent and that the solution of the problem of current reinforcing by such circuits depends upon the securing of synchronous and harmonious as well as cumulative reinforcing action.

Where in the claims I refer to the repeater-receiver element and the repeatertransmitter element as being magnetically independent each of the other What I mean is such construction that the coils or windings of one do not act upon the coils or windings of the other in any except the desired manner, so that they are free from operative interference. This in general means (since the coils necessarily have magnetic cores) that the magnetic cores of the respective elements are separate from each other, whereby the magnetic flux set up by the receiving instrument is not directly operative upon the transmitting element, the latter being designed to be controlled by an independently created magnetic flux.

Having, therefore, fully described my invention in its preferred form and the principles and methods of operation of the same, without limiting myself to the precise forms of apparatus or particular circuit arrangements herein disclosed, which obviously may be varied in many ways by those skilled in the art, what I desire to claim as my invent1on is:

1. In combination with a telephone system main line and its terminal station in strumentalities, a line-actuated line-current reinforcing arrangement operatively related by undivided series connection to said line and free of bridge connection therewith.

2. In combination with a telephone line system and its terminal station instrumentalities, a conductor operatively related to said system and energized by voice-caused line-currents and a current reinforcing arrangement operatively related by undivided series connection to said conductor and free of bridge connection therewith.

3. In combination with a telephone system main line and its terminal station instrumentalities, a line-actuated line-current reinforcing arrangement comprising a receiving element and a transmitting element operated thereby, said receiving element being serially related to said line and said transmitting element being also serially related to the same side of said line.

4. In combination with a telephone system main line and its terminal station instrumentalities, a line-actuated line-current reinforcing arrangement comprising a receiving element and a transmitting element operated thereby, said receiving element being serially related to said line and said transmitting element being also serially related to said line, and being each magnetlcally in dependent of the other.

5. In combination with a telephone system main line and its terminal station instrumentalities, a line-actuated line-current reinforcing arrangement comprising a receiving element and a transmltting element operated thereby, said receiving element being at serially related to said line and said trans- -mittinga element being also serially related to said line, each by undivided series connection to said line.

6. In combination with a telephone system main line and its terminal station instrumentalities, a line-actuated line-current reinforcing arrangement comprising a receiving element and a transmitting element operated thereby, said receiving element be ing serially related to said line and said transmitting element being also serially related to said line, each by undivided series connection to said line, said receiving and transmitting elements being each magnetically independent of the other.

7 In combination with a telephone system main line and its terminal station instrumentalities, a line-actuated line-current reinforcing arrangement comprising a receiving element and a transmitting element operated thereby, said receiving element being serially related to said line and said transmitting element being also serially related to said line, each by undivided series connection to said line, said receiving and trans mitting elements being each magnetically independent of the other, and said reinforcing arrangement being free of bridge or split circuit relation to said line.

8. In combination with a telephone line system and its terminal station instrumentalities, a conductor operatively related to said system and energized by voice caused line-currents, a current-reinforcing arrangement comprising a receiving element and a transmitting element operated thereby, said receiving element being serially related to said conductor and said transmitting element being also' serially related to the same side of said conductor.

9. In combination with a telephone line system and its terminal station instrumentalities, a conductor operatively related to said system and energized by voice-caused line currents, a current-reinforcing arrangement comprising a receiving element and a transmitting element operated thereby, said receiving element being serially related to said conductor and said transmitting element being also serially related to said conductor and being each magnetically independent of the other.-

10. In combination with a telephone line system and its terminal station instrumentalities, a conductor operatively related to said system and energized by voice-caused line-currents, a current-reinforcing arrangement comprising a receiving element and a transmitting element operated thereby,said receiving element being serially related to said conductor and said transmitting element being also serially related to said conductor, each by undivided series connection to said conductor.

11. In combination with a telephone line system and its terminal station instrumentalities, a conductor operatively related to said system and energized by voice-caused line-currents, a current-reinforcing arrangement comprising a receiving element and a transmitting element operated thereby, said receiving element being serially related to said conductor and said transmit- I ting element being also serially related to said conductor, each by undivided series connection to said conductor, said receiving and transmitting elements being each magnetically independent of the other.

12. In combination with a telephone line' system and its terminal station instrumentalities, a conductor operatively related to said system and energized by voice-caused line-currents, a current-reinforcing arrangement comprising a receiving element and a transmitting element operated thereby, said receiving element being serially related to said conductor and said transmitting element being also serially related to said conductor, each by undivided series connection to said conductor, said receiving and transmitting elements being each magnetically independent of the other and said reinforcing arrangement being free of bridge or split circuit relation to said con ductor.

13. In a closed circuit alternating current telephone system, in combination with the line, repeater instrumentalities comprising an initially-energized receiving magnet connected to be operated by received line currents, a conductor with a direct current and having a variable resistance device in series adapted to be variably controlled by said receiving magnet, whereby the opposite phases of received current oppositely affect said direct current flow, and inductive repeater transmitting means energized by the variations of said direct current and connected to re-impress on said line a second alternating current, the circuit connections in the repeating instrumentalities and between such instrumentalities and the line being such that each receiver-caused variation of said direct current tends to produce through the repeater-transmitter, the line, and the repeater-receiver, a harmonious and similar variation of said direct current and the magnetic cores of the repeater receiving and inductive repeater transmitting means being structurally and magnetically independent, each of the other.

14. In a closed circuit alternating current telephone system, in combination with the line, repeater instrumentalities comprising an initially-energized receiving magnet connected to be operated by received line currents. a conductor with a direct current and having a variable resistance device in series adapted to be variably controlled by a vibratory armature in the field of said receiving magnet, whereby the opposite phases of received current oppositely affect said direct current flow, and inductive repeater transmitting means energized by the variations of said direct current and connected to re-impress on said line a second alternating current, the circuit/connections in the repeating instrumentalities and between such instrumentalities and the line being such that each receiver-caused movement of said armature tends to produce through the repeater-transmitter, the line, and the receiving magnet a movement of said armature in the same direction and the magnetic cores of the repeater receiving and inductive repeater transmitting means being structurally and magnetically inde. pendent, each of the other.

15. In a telephone system, the combina tion with a transmitting and a receiving device, and an intermediate continuous main line circuit, of a repeating circuit, means serially associated with the main line circuit for producing current variations in the repeating circuit to correspond to energy variations in the telephone circuit, and means inductively related to the repeating circuit and serially but not inductively associated with the current-variation-producing means, for reinforcing the energy passing through said current-variation-producing means.

16. A telephone system having a telephone circuit, a second circuit having a constant source of electro-motive force, electro-magnetic means for causing current variations in the second circuit, suitable windings in said telephone circuit for inductively energizing said electro-magnetic means, and windings also in said telephone circuit in series with said other windings but noninductively associated therewith for inductively transmitting to the telephone circuit the current variations of said second circuit.

17. In a telephone system, the combination with a transmitting and a receiving device, and a continuous main circuit. line between the same, of a repeating circuit inductively related to one side thereof, a current varying medium associated with said repeating circuit, and means serially associated with the same side of said line circuit to actuate said current varying medium for reproducing current undulations of the line circuit in the repeating circuit.

18. In a telephone system, the combination with separated stations, of a line circuit connecting the two, a source of electrical energy therefor, and a repeating circuit between the stations having a current varying medium and in repeating and reinforcing relation to one side of the line circuit only to reproduce the energy undulations transmitted in either direction from one station to the other.

-' energy thereto,

the combination With a transmitting circuit,

having outgoing and return sides, of a local circuit inductively related to but one side thereof, a source of substantially constant current for said local circuit, and means serially related to the same side of the transmitting circuit, and operated by the energy variations of the latter for establishing the current undulations in the local circuit corresponding to the energy Variations in the transmitting circuit.

21. In a telephone system, the combination with terminal stations and a main line circuit between the same, of an intermediate repeating circuit operatively related to one side only of the main line circuit for the production of current variations in the repeating circuit corresponding to energy variations in the telephone circuit, said repeating circuit being also operatively related to the same side of the main line circuit for the reinforcement of the energy passing therethrough.

22. A telephone system comprising terminal stations having transmitting and receiving instruments, main line circuit between the same having outgoing and return sides, an intermediate repeating circuit, means operatively related to one side of the telephone circuit only, for causing current variations in the repeating circuit corresponding to energy variations in the telephone circuit, and means operatively related to the same side of the telephone circuit for transmitting to the telephone circuit the current variations of the repeating circuit.

23. In a telephone system, a main line circuit and a reinforcing circuit serially related to but one side thereof and provided with a carbon contact current varying device, operated by the current undulations of the main line, for reinforcing the latter.

24. In a system for the transmission of electrical energy, a main line, a local circuit and means for supplying electrical electro magnetic means adapted to be operated by thecurrent variations of said main line to produce in said local circuit current undulations harmonious with those of said main line, and magnetically separate means serially related to said local circuit and to said main line for producing in the latter current undulations proportional to and harmonious With those of said local circuit.

25. A telephone system comprising a main line, a plurality of stations connected thereby, each having transmitting and receiving instruments, a local circuit operatively related to said main line having a local. source of electrical energy, an electro-magnetic device adapted to be operated by the main line energy, and to produce in said 10- cal circuit current variations harmonious with the telephone current of the main line, and an electro-magnetic device adapted to be actuated by said local circuit to produce current influences in the main line harmonious with those produced in said local circuit and transmitting them in either direction from said local circuit, said devices being in series relation to said main line.

26. A telephone system comprising a main line, a plurality of stations connected thereby, each having transmitting and receiving instruments, a local circuit operatively related to said main line having a source of electrical energy, an electro-magnetic device adapted to be operated by the main line energy, and to produce in said local circuit current variations harmonious with the telephone current of the main line, and an electro-magnetic device adapted to be actuated by said local circuit to produce current influences in the main line harmonious With those produced in said local circuit and transmitting them in either direction from said local circuit said devices being in series relation to said main line and free from magnetic relation to one another.

27. In a telephone system having terminal stations and a connecting main line, the combination With a continuous fixed main line section of a two-Way repeating or reinforcing system, the said reinforcing system being serially related to said main line section and freed from bridged connection therewith and said reinforcing system comprising an electro-magnetic receiving element and a magnetically independent electro-magnetic transmitting element and beingadapted to receive current impressions from the main line and to re-impress on said main line harmonious repeater-system-caused current impressions.

28. In a telephone system having terminal stations and a connecting niain line, the combination With a continuous fixed main line section of a fixed circuit two-way repeating instrument, serially related to said main line section and freed from bridge relation thereto, said repeating instrument being adapted to respond to the current variations in the main line and said repeating instrument comprising a receiving portion, including F I luv therein a magnetic core and its winding,

adapted to be energized by said main line current variations, and a transmitting portion, including therein an auxiliary circuit with a source of energy therefor and a resistance-varying device therein adapted to respond to the magnetic action of said core and electro-magnetic means adapted to be actuated by said auxiliary circuit and to inductively cause the re-impression on said main line of current variations harmonious with the action of said resistance-varying device, said core and its winding being magnetically independent of said last mentioned electro-magnetic means.

In a telephone system having terminal stations and a connecting main line, the combination of a continuous fixed main line section and a fixed circuit two-way reinforcing instrument with its circuits, comprising an eleetro-magnetic receiving element, with its helix serially related to said main line section, and an electro-magnetic transmitting element adapted to be actuated through the actuation of said receiving element, said transmitting element being also serially related to said main line and adapted to reimpress thereon current variations harmonious with those received by said receiving element, said receiving and transmitting elements being magnetically independent.

30. In a telephone repeating system, the combination with a telephone line, of a repeating agency having magnetically operatively independent receiving and transmitting elements serially related to the said line.

31. In a telephone repeating system, the combination with a telephone line, of a repeating agency having inductively independent receiving and transmitting circuits serially related to the said line.

32. In a telephone system, the combination with a telephone line, of reinforcing devices comprising magnetically independent receiving and transmitting elements, the receiving element having its operating circuit serially related to the line, and the transmitting element having its controlled circuit serially related to the line.

33. In a telephone system, a main line circuit and a reinforcing circuit serially related to but one side thereof, and provided with a current varying device operated by the current undulations of the main line for reinforcing the latter.

3%. In a telephone system, the combination with a transmitter 23, a receiver 1', the main line a, the receiving element h and the transmitting element 9, the two latter elements being serially related to the line and magnetically independent of each other.

35. In a telephonic circuit, in combination with the main line between the terminal sta ions, a reinforcing instrument, comprising magnetically independent but operatively associated receiving and transmitting serially related to the main line and both the receiving and the transmitting element of the reinforcing instrument being in undivided series relation to its actuated line.

37. In a telephonic circuit, in combination with the main line between the terminal stations, a reinforcing instrument, comprising magnetically independent but operatively associated receiving and transmitting ele ments, the reinforcing arrangement being serially related to the main line and the receiving element and the transmitting element being in undivided series relation respectively to the actuating line and the actuated line.

38. Means for increasing the amplitude of variation of a varying current on a conductor, embodying, in combination with said conductor, a device energized by such conductor and means controlled by said device and in undivided series with said conductor.

39. Means for increasing the amplitude of variation of a varying current on a conductor, embodying, in combination with said conductor, an electro-magnetic device having its winding in series with said conductor and current-varying means controlled by said device and in undivided series relation with said conductor.

40. The combination with a telephone system main line and its terminal station instrumentalities, a line actuated line current reinforcing arrangement operatively related 

